1. Field of the Invention
The present invention relates to forming conductor circuit patterns on electronic substrates such as multilayer ceramic substrates and, more particularly, to forming metal conductor circuit patterns on an unsintered greensheet used to make the multilayer ceramic substrate.
2. Description of Related Art
Ceramics have found widespread use in the electronics industry as a substrate for integrated circuit packages. In general, metalized circuit patterns are applied to a ceramic substrate which is in the form of an unsintered greensheet, and a plurality of the metalized ceramic greensheets are stacked and laminated and co-sintered to create a monolith of substrate and three-dimensional metal circuitry. The ceramic greensheets are constructed by combining ceramic particles and organic binders and forming into unfired, or xe2x80x9cgreensheetxe2x80x9d, tape.
The casting of suspensions of ceramic material to form layers or greensheets which are then laminated and sintered to make a ceramic substrate electronic article is well-known in the art. The doctor blade method is one method for making a ceramic greensheet and typically, ceramic powder is mixed with an organic solvent, a plasticizer and a binder forming a slurry, the slurry is cast in a regulated thickness on a carrier film with the aid of a doctor blade, and the applied layer of the slurry and carrier film is then dried. The ceramic containing formula typically uses a ceramic such as alumina and a butyral type resin like polyvinyl butyral as the binder.
Once the greensheets are formed, via holes are formed in a predefined pattern in the greensheet and the via holes then filled with a conductive paste. Metal lines in a form of circuitry are then formed on the surface of the greensheet by screening or extrusion printing on the conductive paste. The conductive paste is formed of a suitable particulate metallic material such as molybdenum which will withstand the subsequent sintering process. The metalized sheets are then stacked, laminated and fired in an appropriate atmosphere to form a monolithic MLC substrate with a complex internal circuitry.
The process of extrusion or screen printing to create conductive patterns using conductive paste has several drawbacks however. These processes are typically referred to as wet processes and these type processes can distort the dimensions of the greensheet as the solvents and oils in the metallic paste are absorbed into the greensheet. Further, after screening, the sheets must be dried in an oven which adds another process step and inherent problems into the circuitry forming process. These wet type processes also generate large amounts of waste chemicals and need costly treatment and disposal processes.
The use of a wet screening process also makes it commercially impractical to form a conductive circuit pattern on the greensheet which is stratified or graded, e.g., in conductivity, in a plane transverse to the circuit design. Grading of the conductive path or feature is important for certain electronic components as discussed hereinbelow and using a wet screening process would require a first screening with a bottom layer paste and then drying the screened paste. A second screening pass would then be made with a second type paste and then drying the second layer. Such a screening process would require perfect conductor alignment which is difficult if not impossible. In manufacturing multilayer substrates it is important to use processes which provide high productivity, high yield, low cost and pass the necessary electrical tests.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a method for forming a metalized circuit pattern on a greensheet, other electronic component substrate or any other substrate which minimizes many of the problems of the wet processes of the prior art and provides a patterning method having high productivity, high yield and low cost.
It is another object of the present invention to provide a method for making a multilayer ceramic substrate electronic component wherein the circuitry on the substrate layers is formed using a patterning method which has high productivity, high yield and low cost.
A further object of the present invention is to provide a method for making a metal containing transfer sheet for forming metalized circuit patterns on a greensheet, other electronic component substrate or any other substrate.
It is yet another object of the present invention to provide an apparatus for forming a metalized circuit pattern on a greensheet, other electronic component substrate or any other substrate.
An additional object of the present invention is to provide an apparatus for making a multilayer ceramic substrate electronic component.
It is further object of the present invention to provide a metalized circuit patterned greensheet which is made using a patterning method providing high productivity, high yield and low cost.
It is an additional aspect of the present invention to provide a greensheet, electronic component substrate or other substrate containing a conductive metal pattern formed on the substrate surface in a desired circuit pattern wherein the conductive pattern is layered with different materials or vertically graded in conductivity or other properties.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The above and other objects and advantages, which will be apparent to one of skill in the art, are achieved in the present invention which is directed to, in a first aspect, a method for making metalized circuit pattern; on a greensheet or other electronic component substrate comprising:
forming a metal containing transfer sheet comprising a metal powder and a binder;
applying the metal containing transfer sheet on the surface of a greensheet or electronic component substrate;
transferring and adhering a portion of the metalized transfer sheet in a desired metalized circuit pattern from the metal containing transfer sheet to the greensheet and forming the metalized circuit pattern on the greensheet surface; and
removing the remainder of the metal containing transfer sheet from the greensheet leaving the patterned greensheet product.
In a further aspect of the invention the desired circuit pattern is transferred from the metal containing transfer sheet to the greensheet or other electronic component substrate by heat, pressure, stamping, laser, or other similar transfer methods or combination of methods.
In a further aspect of the invention multilayer ceramic electronic component substrates are made by a method comprising:
providing a plurality of greensheet substrates suitable for forming into a multilayer ceramic substrate;
forming a metal containing transfer sheet comprising a metal powder and a binder;
applying the metal containing transfer sheet on the surface of the greensheet;
transferring and adhering a portion of the metal containing transfer sheet in a desired pattern from the metal containing transfer sheet to the greensheet forming the desired circuit pattern on the greensheet surface;
removing the remainder of the metal containing transfer sheet from the greensheet leaving the greensheet having the desired circuit pattern thereon;
repeating the above procedure for the number of greensheets to be used to make the multilayer ceramic substrate;
stacking the pattern containing ceramic greensheets; and
laminating and sintering the stacked ceramic greensheets forming the multilayer ceramic electronic component substrate.
In another aspect of the invention an apparatus is provided for making a greensheet having a metalized circuit pattern thereon comprising:
means to hold and support a greensheet;
means to hold and support a metal containing transfer sheet on the greensheet, the metal containing transfer sheet comprising a metal powder and a binder;
means to transfer and adhere a portion of the metal containing transfer sheet to the greensheet in a desired pattern on the greensheet surface; and
means to remove the remainder of the metal containing transfer sheet not transferred to the greensheet leaving a metalized patterned greensheet having the desired circuit pattern thereon.
In another aspect of the invention the transfer means may be a punch (stamp), laser, raised roller, heat, or other such transfer means or combination of means which transfers a portion of the metal containing transfer sheet to the surface of the greensheet in a desired circuit pattern and leaves the remainder of the metal containing transfer sheet.
In a further aspect of the invention metalized circuit patterned greensheets and other electronic component substrates are provided which are made using the method and apparatus of the invention.
In a further aspect of the invention the metalized pattern on a greensheet or other substrate may be functionally graded (e.g., conductivity, etc.) in vertical cross section using a functionally graded metal containing transfer sheet so as to provide an electronic component in which the metalized circuit design has various properties across its cross-section and therefore may provide various functions in the electronic component. In another aspect, glass and/or ceramic can be included in the metal containing transfer sheet to provide additional transfer sheet bonding properties and adhesive properties for adhering the transferred sheet to the substrate.
In an additional aspect of the invention metal containing transfer sheets are provided for transferring a metal pattern onto a substrate such as a greensheet.